Bis(3,5-dimethylpyrazol-1-ato) zirconium complexes as precursors for ethylene polymerisation upon activation with MAO: Syntheses, characterisation and X-ray molecular structure of [Zr(η2-3,5-Me2Pz)2Cl2(η1-3,5-Me2PzH)2] · (3,5-Me2PzH) and [Zr(η2-3,5-Me2Pz)

The bis(3,5-dimethylpyrazol-1-ato) zirconium complex [Zr(η2-3,5-Me2Pz)2(NMe2)2(NHMe2)2] (2) is obtained by treatment of [Zr(NMe2)4] with 2 equiv. of 3,5-dimethylpyrazole 1. The reaction of the [ZrCl4(THF)2] adduct with 2 equiv. of the potassium salt of 1 affords the dichloro derivative [Zr(η2-3,5-Me2Pz)2Cl2]n (3), while reaction with 4.1 equiv. of 1 in the presence of 2.1 equiv. of NEt3 affords the dichloro pyrazole adduct [Zr(η2-3,5-Me2Pz)2Cl2(η1-3,5-Me2PzH)2] (4). Treatment of [Zr(CH2Ph)4] with 2 equiv. of 1 gives the dibenzyl complex [Zr(η2-3,5-Me2Pz)2(CH2Ph)2] (5) via alkane elimination. Compound 4 presents fluxional behaviour in CDCl3 solution, which was studied and quantified by variable-temperature proton NMR experiments. All compounds were characterised by routine analyses and the molecular structures of 4 and 5 were established by single-crystal X-ray diffraction studies. The performance of precursors 3 and 5 was evaluated in ethylene polymerisation upon activation with MAO.

Graphical abstractBis(3,5-dimethylpyrazol-1-ato) zirconium(IV) derivatives were synthesised by various routes such as amine-, salt-, and alkane elimination. All compounds were identified by structural methods. The performance of the dichloro and dibenzyl zirconium(IV) precursors in ethylene and propylene polymerisations upon activation with MAO was evaluated.Figure optionsDownload full-size imageDownload as PowerPoint slide